A 'Net Speed Increase

SCIENCE

Using Wiring That's Already In Most Homes, Phone And Cable Companies Are Adapting Digital Technology To Provide Consumers With Lightning-fast Internet Service, With True Multimedia And Movies-on-demand Not Far Behind.

July 27, 1997|JIM WEBB/Staff graphic

Analog modems

including 33.6K and 56K modems

Analog modems convert digital data to audio data that can be sent over standard phone lines. Phone lines are simply two copper wires connecting your home to the phone company; however, telephone companies filter the range of signals used on those wires. This works well for normal conversations but limits the amount of data that a modem can pass.

33.6K modem is fastest analog

A 33.6K modem squeezes 33,600 bits (4.1 kilobytes) per second into the audio range. Compressing the data can improve performance, but line noise and poor-quality conncetions usually lower the data rate to 30,000 bits (3.6 kilobytes) per second or less.

Only audio can pass

Analog modems convert computer data into audio signals that can pass through the phone company's switchboard. The phone comapny converts the audio to digital signals used on trunk lines to the Internet

Least expensive of the fast

33.6K modems cost from about $90 to $180. Internet service providers generally charge about $20 a month for unlimited access.

Data ceiling

A 33.6K modem uses the most data the telephone audio band can theoretically hold.

56K modem speaks half-digital

If an Internet service provider has a digital connection to the phone company, as many do, they can send digital information directly to users. Users must still use analog technology to send data.

Receive a digital

Users can receive digital data from an Internet service provider at up to 56,000 bits (6.8 kilobytes) per second.

Send in analog

Users still must send data as converted audio signals at only 33,600 bits (4.1 kilobytes) per second.

Cable joins in

Some cable companies, using their own direct connection to the Internet, have begun offering cable modem service.

No one standard

Modem companies have developed two kinds of 56K modem technology, X2 and K56Flex. Though they operate at the same speed, they won't work with each other, so a user must have the same type of 56K modem as the Internet service provider to use the 56K speed advantage.

Costs involved

Modems using 56K technology cost from about $120 to $220. Internet service providers generally charge about $20 a month for unlimited access.

FCC's speed trap

Current FCC rules limit the speed of 56K modems to 53,000 bits (6.4 kilobytes) per second. If this rule is lifted, software updates will allow the modems to run at top speed.

When fast modems go slow

Just because a modem is fast doesn't mean a user can down load information at top speed. All modems are susceptible to line noise and poor connections, which often slow the flow of data. Also, because the Internet is a decentralized network of computers passing information to one another, a busy or slow connection among any of them could delay data on its way to a user, and sites themselves may have slow connections. In the case of ADSL and cable modems, the modems may work faster than many sites can send data.

For more on why Web slowdowns occur, see related BusinessSunday article, Page 1F.

Digital modems

Including ISDN, ADSL and cable modems

Using special equipment, digital signals can be passed along existing phone wires. With digital signals, much more data can pass and multimedia uses like video-on-demand become possible. Digital lines are best suited to urban areas, as the complex signals break up beyond three or four miles from telephone company equipment.

ISDN lines widely available

Available across the country, Integrated Services Digital Network lines are the current standard for consumer digital lines.

Digital lines bypass audio circuits

Digital lines use switching systems installed at the phone company that let regular phone wires tap directly into the digital part of the telephone company and Internet service providers.

Uses ISDN phones

Special ISDN phones, fax machines and modems must be used on an ISDN line.

Two data channels

An ISDN line uses two data channels. Each channel can be used for digital voice data, fax data or computer data, or combined to provide computer data at 128,000 bits (15.6 kilobytes) per second. Channels switch on the fly, so a user can receive a digital phone call or fax while online.

Asymmetric Digital Subscriber Lines also require some rewiring at the phone company but create a very fast connection. Until consumer uses like video-on-demand become feasible, ADSL will mostly be used to connect computer networks together.